Shock absorbing device



Sept. 6, 1960 F. c. scHusTE-R sHocx ABsoRBING DEVICE Filed May 2, 1957 w//// l 7 na 7 /f J United States Patent O SHOCK ABSORBING DEVICE Frank C. Schuster, Chicago, lll., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Filed May 2, 1957, Ser. No. 656,591

Claims. (Cl. IS7-9) This invention relates to the use of shock absorbing devices in a hydraulic system of a lifting mechanism to cushion loads carried by the mechanism against shock transmitted through the hydraulic uid. And particularly, this invention relates to the use of a gas type accumulator in a hydraulic lifting ram such as is used on a lift truck.

The fork truck industry has for some time been faced with a problem of protecting fragile loads handled by the truck against shock. Heretofore, it has been suggested that hydropneumatic accumulators be placed in the hydraulic supply line to the lift cylinder between the latter and the control valve. One such accumulator uses an outer metal shell and an inner flexible bag lled with gas, the space between the metal shell and the bag being in communication with the hydraulic line to the lift cylinder. Although the gas filled bag type of accumulator arrangement has been somewhat effective in reducing shock transmitted to the transported cargo, this prior arrangement is expensive and requires additional mounting space on the truck.

It is desirable to provide an accumulator that separates the compressible gas from the hydraulic liuid, is easy to install, remove and service and is as near as possible in the hydraulic system to the place where the shock is applied. The present invention contemplates the provision of an accumulator Within a hydraulic ram and in such location takes up a minimum space.

It is an object of this invention to provide a shock absorbing device that takes care of the hereinbefore mentioned difficulties and requirements in an entirely satisfactory manner.

More specifically, it is an object of this invention to provide an accumulator that does not take up additional space on the truck, is readily accessible for recharging with gas and is inexpensive.

Further, it is an object of this invention to provide an accumulator inside that component of the hydraulic system which is interposed between the load and the truck chassis.

Further, it is an object of this invention to provide an accumulator of the piston type in the hydraulic lift cylinder of a lift truck.

These and other objects and advantages of this invention will become apparent to those skilled in the art when -the following description is read in conjunction with the drawings, in which:

Fig. 1 is a perspective view of a lift truck of the type in which the present invention is advantageously used;

Fig. 2 is a vertical section view of the hydraulic lift ram of the lift truck of Fig. 1 in which one embodiment of this invention is incorporated; and

Fig. 3 is a vertical section view of the hydraulic lift ram incorporating a second embodiment of the present invention.

Referring to Fig. 1, a conventional fork truck 6 s illustrated. This fork truck is of the type used for elevating and transporting cargo on its forks 7 which are ICC secured to a vertically movable carriage 8. The carriage 8 is reciprocably mounted on an inner mast 9 and the inner mast 9 is reciprocably mounted on an outer mast 11 in a conventional manner. A single acting hydraulic ram 12 carries a cross shaft 13 at its upper end. The cross shaft 13 rotatably supports a pair of sprockets 14 by which a pair of chains 16 are actuated. The lower end of the ram 12 and the outer mast 11 are supported on the truck chassis. The forward lower ends of the chains 16 are secured to the carriage 8 and the other ends of the chains 16 are secured in a conventional manner to the outer mast 11. The cross shaft 13 is secured to the inner mast so as to elevate it upon expansion of the ram 12.

The cargo (not shown) carried by the: forks 7 is elevated or lowered by expansion and contraction of the ram 12 and shocks transmitted to the chassis of the truck upon travel over uneven oors or terrain, are transmitted through the hydraulic ram 12 to the cargo being carried. Also shock loads may be imposed upon the cargo by quick closing of the hydraulic ram control valve, not shown, thereby causing instantaneous stopping of the movement of the carriage 8. Operation of the truck over uneven pavement or rough ground may cause breakage of fragile cargo.l If liquid is being transported in open containers, the bouncing over uneven floors may spill the liquid.

The shock absorbing devices shown in. Figs. 2 and 3 cushion the jouncing effect upon fragile cargo such as glassware and crated eggs. These shock. absorbing devices also reduce operators fatigue and improve performance by allowing higher speeds of operation. Also, the hydraulic and mechanical components employed to support the cargo last longer because they are subjected to less shock loading.

Referring to Fig. 2, the hydraulic lift ram 12 is of the type having a pair of open end telescoping cylinders 17, 18. The outer cylinder has a closed bottom through which a hydraulic input passage 19 extends. This input passage is connected to a conventional hydraulic supply system, not shown, which is carried by the truck. The bottom of the outer cylinder 17 is supported on the truck chassis through the outer mast 11. The inner cylinder 18 has its open end in telescoping relation to the open end of the outer cylinder. The inner cylinder 18 which serves as a piston is sealed in fluid tight relation with the outer cylinder 17 by packing 21 held in place by packing retainer 22. The retainer 22 and ring 23 serve as bearing members between the cylinders 17, 18.

A shock absorber assembly 24 is installed within the upper end of inner cylinder or cylindrical piston 18. The shock absorber assembly includes a cap 26 having circumferential threads 27 engaging complementary threads 28 in cylindrical piston 18. An O-ring seal 29 is positioned in a groove 30 to seal the cap to the cylindrical piston 18. The cap 26 has a downwardly extending sleeve portion 31 which is externally threaded to receive a threaded end of a tube 32, the latter extending into the inner cylinder or piston cylinder 18. An O-ring 33 is nterposed between the cap 26 and tube 32 so that they will be in gas tight relation to one another. A cylindrical inward facing surface 34 is formed in the tube 32 and a oating piston 36 is mounted in gas tight engagement with the surface 34. This gas tight sealing engagement is effected through use of an O-ring 37 in a groove 38 in the piston 36. A snap ring 39 of conventional design is fitted into an internal groove 41 in the lower end of tube 32. The snap ring serves as a stop means for preventing withdrawal of the piston 36 from the open end of tube 32. In addition to the cap 26, tube 32, piston 36 and stop means 39, the shock absorber assembly includes a gas valve 42 at the non-telescoping end of cylinder 18.

The valve 42 is screwed into a threaded opening 43 in the cap 26. An upwardly extending cylindrical wall 44 is provided on the top side of the cap 26 in protecting relation to the valve 42, and this cylindrical wall 44 also fits into a circular opening 46 formed in shaft 13 thereby maintaining-the shaft 13 on the upper end of ram 12.

From the foregoing description, it is evident that the accumulator or shock absorber assembly 24 is releasably secured in the upper end of cylindrical piston 18 thereby permitting quick installation and removal. The accumulator can be sold as extra equipment for field installation. It can be filled with a suitable gas such as nitrogen either before or after installation in a hydraulic ram. Since the accumulator fits Within the hydraulic ram the pressure will be equalized on both sides of the tube 32. As hydraulic pressure increases the piston moves upward, as shown in Fig. 2, compressing the gas in the chamber defined by one side of the piston 36, the cylindrical surface 34 and cap 26. Thus in operation there will be a pressure fluid chamber at the lower end of the tube 32 defined by the other side of the piston 36 and cylindrical surface 34.

Referring to Fig. 3, there is shown a second embodiment of the present invention. In this second embodiment a radially inner cylindrical surface 34 is formed in the upper end of the inner cylinder 18' of ram 12. In the process of forming this surface 34 the inner diameter of cylinder 18' is increased leaving a shoulder 47 at the end of the cylindrical surface 34'. This shoulder 47 serves as stop means to prevent the floating piston 36 from downward travel thereby permitting the chamber in the upper end of inner cylinder 18 to be charged with gas at any time. As shown in Fig. 3, the pressure exerted by the gas is greater than the pressure exerted by the fluid in the ram 12.

The cap 26' is similar in construction to that of cap 26 except the threaded sleeve portion 31 of cap 26 is not provided. Elimination of the tube 32 may be preferred in those installations where the inner cylinder 18 is of a suitable material for finishing to receive the piston 36 and its sealing means 37 in gas tight engagement.

This invention provides a shock absorbing device that takes up no additional space on the truck and is in direct communication with the hydraulic fluid in the hydraulic component carrying the cargo.

The accumulator built into the ram, as shown in Fig. 3, or the unit accumulator of Fig. 2 is readily charged with a suitable gas such as nitrogen.

The accumulator 24 is easily installed and removed for servicing, if necessary, and is suitable for field installation as well as factory installation.

The illustrated accumulators are more responsive to the shocks that the hydraulic ram 12 is subjected to since they are within the cylinder rather than in the hydraulic supply line. Also special hydraulic fittings in the hydraulic line are eliminated.

It should be understood that it is not intended to limit the invention to the particular forms and details described hereinabove and that the invention includes such other forms and modifications as are embraced by the scope of the appended claims.

What is claimed is:

1. In a fork lift truck the combination comprising: a mast supported on one end of said truck; a load carrying carriage mounted for vertical reciprocating movement on said mast; an expansible and contractible hydraulic lifting ram mounted on said truck for raising and lowering said carriage including a pair of telescoping hollow cylinders, the telescoping ends of which are open and the nontelescoping ends of which are closed; a cylindrical radially inward facing surface within one of said cylinders; a floating piston reciprocably mounted in sealing engagement with said surface; and a chamber for receiving a compressible gas defined by one axial side of said floating piston, said cylindrical surface and the nontelescoping end of said one of said cylinders, the other axial side of said floating piston being in communication with the pressure fluid within said ram.

2. In a fork lift truck the combination comprising: a mast supported on one end of said truck; a load supporting carriage mounted for vertical reciprocating movement on said mast; an expansible and contractible hydraulic lifting ram mounted on said truck including a cylinder having its bottom end supported on the truck chassis and a cylindrical hollow piston within said cylinder supporting said carriage; and a floating piston within said hollow piston dividing the latter into a gas receiving chamber at its upper end and a pressure fluid chamber at its lower end.

3. In a fork lift truck the combination comprising: a mast supported on one end of said truck; a load supporting carriage mounted for vertical reciprocating movement on said mast; an expansible and contractible hydraulic lifting ram mounted on said truck including a cylinder having its bottom end supported on the truck chassis and a cylindrical hollow piston within said cylinder, said hollow piston supporting said carriage; a tube having an open end and a closed end; means releasably securing said tube within the axially outer end of said hollow piston, and a floating piston reciprocably mounted within said tube, said tube and floating piston defining a gas chamber in the upper end of said tube.

4. In a fork lift truck the combination comprising: a mast supported on one end of said truck; a load supporting carriage mounted for vertical reciprocating movement on said mast; an expansible and contractible hydraulic lifting ram having one end mounted on said truck and its other end supporting said carriage; a tube having an open end and a closed end; means securing said tube Within said ram; and a floating piston reciprocably mounted within said tube, said tube and floating piston defining a gas chamber at the closed end of said tube.

5. In a fork lift truck the combination comprising: a mast supported on one end of said truck; a load supporting camage mounted for vertical reciprocating movement on said mast; an expansible and contractible hydraulic lifting ram having one end mounted on said truck and its other end supporting said carriage; and a floating piston within said ram separating a gas containing chamber from the hydraulic fluid in said ram.

References Cited in the file of this patent UNITED STATES PATENTS 1,074,499 Ensign Sept. 30, 1913 2,379,388 Thornhill June 26, 1945 FOREIGN PATENTS 461,144 Great Britain Feb. 11, 1937 886,413 Germany Aug. 13, 1953 

